Cathode ray tube envelope



Oct. 6, 1959 E. SWEDLUND 2,907,906

CATHODE RAY TUBE ENVELOPE Filed May 18, 1958 v SODA LIME 8 FIG. GLASS l0 LEAD ALKAU GLASS INVENTOR LLOYD E. SWEDLUND United States Patent 2,907,906 CATHODE RAY TUBE ENVELOPE Application May is, 1956, Serial No. 585,669 Claims. c1. 313-64) This invention relates to cathode ray tubes and more particularly to improvements in glass envelopes for cathode ray tubes.

Glass cathode ray tube envelopes of the prior art gen.- erally consist of a tubular neck connected at one end to an enlarged bulb including'a funnel section and a faceplate section through which the screen is viewed. The free end of the neck is closed by a stem through which the tube is exhausted and through which pass and are sealed the leads by which certain of the electrodes of the tube are connected to an exterior power supply.

The faceplate, funnel, and neck of early cathode ray tubes were fabricated by blowing in one piece, by hand. In order to make larger size tubes, the bulbs alone were later hand-blown in one piece with a large, short neck, and sealed to a small diameter neck usually made from drawn tubing. Such bulbs were often irregular in shape and also required skilled glass blowers and much hand work. In an effort to improve quality and speed up production, the faceplate was later formed separately by a pressing operation, and joined to a blown or pressed funnel.

While the pressed glass technique is adaptedto quantity production, the pressed-faceplate type of envelope has certain disadvantages arising from the fact that the glass is generally thicker'and heavier than desired, particularly in the smaller size envelopes, because it is impractical to press in' thinner sections. Also, the separate forming and attachment of the parts requires a relatively large number of manufacturing steps which contribute to increased manufacturing cost. Further, the attachment of the faceplate to the funnel is both time-consuming and expensive.

Accordingly, one object of the present invention is to provide a cathode ray tube envelope having satisfactory faceplate quality for television picture tubes, and whose cost is significantly lower than envelopes of a comparable size in the prior art.

Another object is to provide a cathode ray tube envelope having an improved one piece bulb which particularly lends itself to fabrication. on high speed glass container making machinery.

Another object is to provide an envelope which can be made in large quantities easily, quickly, and at minimum cost.

Another object is to provide an improved television picture tube having minimum weight and maximum viewing area in proportion to its bulb size.

These and other objects of the invention will be apparent from the description following hereinafter, and the scope of the invention will be defined in the appended claims.

Briefly, the foregoing objects are attained in accordance with the present invention by making the bulb of the tube envelope in one piece and of a particular type of glass which is especially suitable for machine-forming on high speed glass container making machinery, while mak- 2 ing the neck portion separately and of a superior electrical insulative properties.

For a more complete description of the invention, reference is made to the accompanying drawing wherein: Figure 1 is an axial sectional view of a television picture tube constructed in accordance with the present ,invention; I

Figure 2 is an enlarged fragmentary axial sectional view of certain portions of the tube of Figure 1 before as sembly;

Figure 3 is a View of the after assembly; and

Figure 4 is a fragmentary axial sectional view of a modified form of the tube of Figure l. 7

Referring to Figure 1, the envelope of the tube consists of a tubular neck 2 joined to and closed by a stem 4 at its rear end, and having a generally conical flaring portion 6 at its front end joined to an enlarged bulb 8 including a funnel section 10 and a somewhat flattened, generally rectangular faceplate section 12. Luminescent screen material 14 is deposited on the interior of the faceplate section of the tube. Within the neck are situated suitable electrodes forming an electron gun and consisting of a cathode 16, heater 18, control grid 20, accelerating grid 22, pre-accelerating anode 24, electrostatic focus electrode 26, and final accelerating anode 28. All of these electrodes. are supplied with suitable operating potentials from a power supply, not shown, through leads 30, all of which are sealed in stem 4 and extend through the stem to the exterior pins 32 of the base 34.

The interior wall of the funnel is provided with a conglass having parts shown in Figure 2,

' ductive coating 36 which extends part way down the neck and is electrically connected to the anode 28 through straps 38. The coating 36 may terminate at its forward end in spaced relation with screen 14, as best shown in Figure 4, or alternatively may extend in a continuous layer across the faceplate 12, as shown at 39 in Figure 1, beneath the screen material 14. In the latter event at least the portion 39 of the coating must be transparent, and may consist for example of tin oxide. Coating portion 39 has the advantage of providing a conductive film adjacent the screen 14 which minimizes the need for sufiicient secondary emission from the screen to prevent positive charge accumulation thereon. This in turn minimizes the thickness of the layer of screen material required, effecting maximum economy in the use of the luminescent screen material itself, as well as contributing to greater uniformity of color and maximum output of light from the screen, and providing optimum picture contrast.

Since coating 36 derives its potential through straps 38 from anode 28, which is in turn adapted to be connected to the power supply through the neck and stem of the tube by one of the leads 30, it will be appreciated that the need for an exterior anode connection passing through the funnel wall of the bulb is eliminated. This avoids the cost of sealing a conductive terminal in the funnel wall, thereby significantly reducing manufacturing cost.

Further in accordance with the invention, the entire bulb portion 8 of the envelope is made from a single integral mass of low cost glass of the type conventionally used to make ordinary glass containers, e.g. soda-lime glass. An exemplary composition for such a glass, in percent by weight is:

{Percent 70-73 13-16 Including up to 3% MgO.

SiO N320 CaO This type of glass is especially suitable for machine forrmng to bulb-like shape on high speed pressing and blowing machinery of the type conventionally employed to make ordinary commercial containers such as bottles, jarsf and the like. Such a bulb therefore has several advantages in that the soda-lime glass is in itself relatively inexpensive, and, because this glass is particularly suitable for use with high speed container-forming machinery, the bulb may be fabricated in large quantities easily, quickly, and with a substantial saving in manufacturing cost. It is contemplated, for example, that the cost of the bulb of the type described may be reduced in comparisonwith those of prior art tubes by a factor of as much as six to one.

' Further in accordance with the invention, the neck of the envelope is made of a glass having relatively high electrical resistivity, e.g. lead alkali glass, so as to afford a high degree of insulation between the interior of the tube andthe deflection apparatus, such as magnetic deflection yoke, not shown, or other accessories outside the tube envelope. The glass of which the neck is made should preferably have a resistivity of from a thousand to a million times that of the bulb glass, for example of the order of 10 ohm-centimeters at a temperature of 100 centigrade. An exemplary composition for such a glass, in percent by weight is:

Percent Si 63 Na O 7.6 K 0 6.0 CaO 0.3 MgO 0.2 PbO 21 B 0 0.2 A1 0 0.6

Although the lime glass of which bulb 8 is made has poorer insulation qualities than might otherwise be desirable, the leads 30 for all of the electrodes, including anode 28 and coating 36 which are at the highest potential, are brought out through the stem 4. This eliminates the usual external anode connection on the bulb 8, and confines the need for material of superior insulation characteristics to the neck 2 and stem 4, where it is satisfied by' the use of suitably high-resistivity lead glass. The coating 36 heretofore described further contributes to the satisfactory performance of the lime glass bulb by conducting away and preventing accumulation on the bulb wall of field distorting charges which might otherwise result from minute electrical leakage through the relatively low resistivity bulb wall.

Once the bulb 3 and neck tube 2 are formed, the entire assembly of the tube is completed in the single step of joining the neck to the bulb. Further in accordance with the invention and to facilitate the joining of the neck to the bulb, the rearward end of the bulb is provided with an outstanding generally cylindrical throat 40, as best shown in Figure 2, having a thickened bead-like or lip portion 42 at its outer end formed with a conical exterior surface 44 substantially coaxial with the bulb axis or the normal to the center of the faceplate 12. The throat 40 and lip 42 can be formed integrally with the bulb at practically no additional cost since a throatlike flash or appendage on the bulb is formed naturally incident to the pressing and blowing operations by which the bulb is formed. By choosing a suitable shape for the pressing and blowing molds, a lip 42 of the shape described and "requiring no further finishing can be formed automatically simultaneously with the forming of the bulb proper. Thus, according to the invention, not only is advantage taken of such a throat-like appendage on the bulb, but a' saving is made in the time and the cost which would otherwise be involved in removing the appendage from the remainder of the bulb.

The flaring portion 6 at the forward end of the neck is likewise formed so that the forward portion of its interior surface 46 is complementary to and rnates'with the surface 44. The neck and bulb are joined by heating the area adjacent the mating surfaces 44, 46 and placing the mating surfaces in contact until the contiguous portions of glass flow and fuse together to form a rigid, mechanically-strong, and leak-proof joint, as best shown in Figure 3.

The particular shape and arrangement of the mating surfaces 44, 46 described facilitates joining of the parts with a minimum of working, either before or during the application of hea t. This is particularly important because it keeps down the amount of heating required, and thereby minimizes stresses in the glass and possibility of breakage. Also minimized is the amount of final annealing required, which is especially desirable in the present instance because the high resistivity neck glass anneals at a diflerent temperature than the bulb glass.

Thus there has been shown and described an improved envelope for cathode ray tubes whose composite construe: tion from container glass and high resistivity glass permits inexpensive, high speed, low cost production on glass container-making machinery. The present invention completely eliminates the expensive and painstaking step heretofore required of joining a faceplate to a funnel portion of a bulb, while providing a bulb of clarity, uniformity and freedom from blemishes. The one piece bulb also may be thinner-walled and lighter in weight, and offers substantially larger viewing areas in proportion to its size than the relatively thick walled, pressedfaceplate tube envelopes of the prior art.

It will be appreciated by those skilled in the art that the invention may be carried out in variousways and may take various forms and embodiments other than the illustrative embodiment heretofore described. It is to be understood, therefore, that the scope of the invention is not limited by the details of the foregoing description, but will be defined in the following claims.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In a cathode ray tube of the type having a luminescent screen adapted to be impinged by electrons, an envelope comprising a one-piece bulb of container glass having an electrical resistivity of 10 to 10 ohm-centimeters at a temperature of centigrade, and a tubular neck connected to said bulb, said neck being of a glass having an electrical resistivity not less than 10 ohmcentimeters at a temperature of 100 centigrade.

2. In a cathode ray tube of the type having a luminescent screen adapted to be excited by electrons, an envelope comprising a one-piece bulb of soda-lime glass, and a tubular neck of lead-alkali glass.

3. A cathode ray tube envelope comprising a one piece bulb portion including a funnel section and a faceplate section of soda-lime container glass whereby said bulb is suitable for forming on high speed glass container-making machinery of the press-blow type, and a tubular neck joined to the bulb, said neck being made of a glass having an electrical resistivity of 10 to 10 times that of the bulb.

4. In a cathode ray tube, a one piece bulb of container glass including a funnel section and a faceplate section, a tubular neck joined to the, bulb and consisting of a glass having a high electrical resistivity relative to the bulb glass, a conductive coating on substantially the entire interior surface of the bulb, the portion of said conductive coating covering at least a part of the faceplate section of said bulb being transparent, and a luminescent screen on the interior of said faceplate section of the bulb overlying a portion of said conductive, coating thereon.

5. In a cathode ray tube, a one piece soda-lime glass bulb having a continuous aperture-free wall including a funnel section and a faceplate section, a lead-glass tubular neck sealed to the bulb, a conductive coating on the interior surface of the funnel section of the bulb, a luminescent screen on the interior of said faceplate section of the bulb, gun electrodes forming an electron gun within said envelope, bias supply leads connected to said gun electrodes and adapted to be connected to a power supply exterior to said envelope, a bias supply lead for said conductive coating adapted to be connected to an exterior power supply, and a lead-glass stem closing the free end of said neck through'which all of said bias supply leads pass and in which all of said leads are sealed.

6. In a cathode ray tube, a one-piece soda-lime glass bulb having a continuous aperture-free wall including a faceplate section and a generally conical funnel section having at its apex end an open throat, an annular lip on the end of said throat formed with an outwardly facing conical sealing surface, a lead-alkali glass tubular neck having at one end an inwardly facing conical sealing surface sealed to said annular lip, a continuous conductive coating covering the entire interior surface of said bulb and extending part Way into said neck, the part of said coating covering at least a portion of said faceplate section being transparent, a luminescent screen on the interior of said faceplate section overlying a portion of the conductive coating thereon, gun electrodes in said neck forming an electron gun, power supply leads for said gun electrodes and said conductive coating extending within said neck and adapted to be connected to an exterior power supply, and a lead-alkali glass stern closing the free end of said neck through which all of said leads extend and in which said leads are sealed.

7. A bulb adapted to form part of a cathode ray tube envelope and adapted to be formed by press-and-blow molding, said bulb consisting of a one piece hollow vessel of soda-lime glass having a faceplate section and a generally conical funnel section formed with an opening at its apex end, and a conical exterior surface on said bulb adjacent the rim of said opening adapted to mate with and be fused to a complementary surface on a tubular neck.

8. In a cathode raw tube envelope, a one piece hollow bulb of soda-lime glass adapted to be formed by pressing and blowing in a mold, said bulb having a faceplate section and a generally conical funnel section formed with an open throat at its apex end, said throat terminating in a mold flash forming an outstanding molded lip having a generally conical exterior surface substantially coaxial with a normal to the center of the faceplate section and adapted to mate with and be fused to a complementary surface on a tubular neck.

9. A bulb adapted to form part of a cathode ray tube envelope, said bulb consisting of a one piece hollow vessel of soda-lime glass having a faceplate section and a generally conical funnel section formed with an opening at its apex end, a conical exterior surface on said bulb adjacent the rim of said opening adapted to mate with and be fused to a complementary surface on a tubular neck, and a conductive coating on substantially the entire interior surface of said bulb, the part of said conductive coating covering at least a portion of said faceplate section being transparent.

10. In a cathode ray tube envelope, a one piece hollow bulb of soda-lime glass adapted to be formed by pressing and blowing in a mold, said bulb having a faceplate section and a generally conical funnel section formed with an open throat at its apex end, said throat terminating in an outstanding molded lip having a generally conica-l exterior surface substantially coaxial with a normal to the center of-the faceplate section and adapted to mate with and be fused to a complementary surface on a tubular neck, and a conductive coating on substantially the entire interior surface of said bulb, the portionv of said conductive coating covering at least a part of said faceplate section being transparent.

References Cited in the file of this patent UNITED STATES PATENTS 1,266,785 Finkbeiner May 21, 1918 2,254,090 Power Aug. 26, 1941 2,504,504 Despois Apr. 18, 1950 2,508,001 Swedlund May 16, 1950 2,585,614 Bailey Feb. 12, 1952 2,629,206 Giffen Feb. 24, 1953 2,699,014 Van Steenis J an. 11, 1955 2,740,062 Swedlund Mar. 27, 1956 2,767,342 Anthony Oct. 16, 1956 FOREIGN PATENTS 466,426 Great Britain May 27, 1937 602,804 Great Britain June 3, 1948 

